Gray Wolves Under the Endangered Species Act (ESA): Distinct Population Segments and Experimental Populations

Kristina Alexander
Legislative Attorney

M. Lynne Corn
Specialist in Natural Resources Policy

The wolf was among the first animals protected under the Endangered Species Preservation Act, a predecessor to the current Endangered Species Act (ESA). In 1978 the gray wolf was listed as endangered in all of the conterminous 48 states except Minnesota, where it was listed as threatened. With the exception of experimental populations established in the 1990s, the protections for the gray wolf have been diminishing since that date, as wolf populations have increased in some areas. The use of distinct population segments (DPSs), a term created in the 1978 ESA amendments, has played a role in that reduced protection. DPSs allow vertebrate species to be divided into distinct groups, based on geography and genetic distinctions. 

ESA protection for DPSs has changed back-and-forth since the first DPSs—Western and Eastern—were proposed in 2003. In 2004, the U.S. Fish and Wildlife Service (FWS) determined that those DPSs no longer needed the protection of the ESA and so were delisted. The Western and Eastern DPS designations and delistings were nullified by courts. In 2007, FWS designated and delisted the Western Great Lakes DPS, and in early 2008, FWS designated and delisted the Northern Rocky Mountains DPS. However, courts found both delistings flawed and vacated the rulemaking. In December 2008 FWS returned the wolves in the Western Great Lakes and parts of the Northern Rocky Mountains areas to their former protected status, eliminating the DPSs. That same rulemaking redesignated wolves in south Montana, southern Idaho and all of Wyoming as "nonessential experimental populations," which they were prior to the DPS efforts. The rulemaking took effect on December 11, 2008, meaning it appears to be outside the scope of White House Chief of Staff Rahm Emanuel's memorandum of January 20, 2009, halting the effect of all non-final regulations pending further review. FWS published a notice to delist the Western Great Lakes DPS in April 2009, but was sued and returned the population to its previous status. Also in April 2009, FWS delisted the Northern Rockies population except for in Wyoming. 

This report analyzes the DPS designation process as it is applied to the gray wolf. It also examines experimental populations of wolves under the ESA and their protections. As part of its oversight responsibilities, Congress has conducted hearings on the Fish and Wildlife Service's application of science to endangered species.


Date of Report: April 28, 2010
Number of Pages: 19
Order Number: RL34238
Price: $29.95

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